Recently, a semiconductor IC (integrated circuit) has been operated at a low level voltage. In this situation, there is a problem because the low level voltage is not sufficient for an oscillator provided in the semiconductor IC, especially at the start of oscillation, so that the oscillation can not be started. Accordingly, an oscillation inducing circuit is used in the semiconductor IC to obtain a boosted voltage supplied to the oscillator.
A conventional oscillation inducing circuit comprises a plurality of transfer gates which are turned on and off in response to received clock signals. A capacitor accumulates electric charges from a power supply in accordance with the turning-on and off of the transfer gates.
In operation, the capacitor is charged by a voltage of the power supply applied alternately on two opposite electrodes, when the transfer gates are turned on and off synchronously with the clock signals, so that a boosted voltage which is larger than the power supply voltage is obtained at one of the two opposite electrodes of the capacitor. The boosted voltage is applied to an oscillator which is driven to provide a predetermined oscillation signal.
However, the conventional oscillation inducing circuit has a disadvantage in that an operation can not be carried out, unless clock signals are available thereto. Therefore, an oscillator is absolutely required to have been operating at the starting time of the operation of the conventional oscillation inducing circuit.